CHAPTER XXX 



THE STRUGGLE FOR EXISTENCE AND THE SURVIVAL 

 OF THE FITTEST 1 



455. Weeds. Any flowering plant which is trouble- 

 some to the farmer or gardener is commonly known as a 

 weed. Though such plants are so annoying from their 

 tendency to crowd out others useful to man, they are of 

 extreme interest to the botanist on account of this very 

 hardiness. The principal characteristics of the most suc- 

 cessful weeds are their ability to live in a variety of soils 

 and exposures, their rapid growth, resistance to frost, 

 drought, and dust, their unfitness for the food of most of 

 the larger animals, in many cases their capacity to accom- 

 plish self-pollination, in default of cross-pollination, and 

 their ability to produce many seeds and to secure their 

 wide dispersal. Not every weed combines all of these 

 characteristics. For instance, the velvet-leaf or butter- 

 print, 2 common in cornfields, is very easily destroyed by 

 frost ; the pigweed and purslane are greedily eaten by pigs, 

 and the ragweed by some horses. The horse-radish does 

 not usually produce any seeds. 



It is a curious fact that many plants which have finally 

 proved to be noxious weeds have been purposely intro- 

 duced into the country. The fuller's teasel, melilot, 

 horse-radish, wild carrot, wild parsnip, tansy, oxeye daisy, 



1 See Darwin's Origin of Species, Chapters III and IV. 



2 Abutilon Avicennse. 



387 



